There is no strict verse in the Qur'an which clearly shows us that the blood money of a women is half that of a man. However, narrations both in Shi'ite and Sunni traditions exist regarding this case. For instance, Imam Sadiq(a.s) says that,

2 Answers
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When is blood money applied?

Blood money is not a price for the person killed; it is a financial compensation for the harm caused to the family of the victim, to be paid by the killer if the death was accidental, or not intentional.

why the blood money of a Women is half of the blood money of a man in Islam?

because the financial loss to the family by the demise of a male member is greater compared to the loss of the female member.

Does this imply value of women is less than that of men?

No, because

blood money is financial compensation, NOT the body-price of the deceased

in case of planned murder, the killer is punished by death, regardless of the gender of the killer and the killed.

In the case of the unintentional death of one person among a husband and a wife, who receives the financial compensation? The other one. That is: A wife receives twice as much financial compensation a husband would receive.

So this rule of Islam is absolutely concerning women, and absolutely logical.

This rule is about any unintentional causing of a death, and not necessarily containing criminal recklessness or negligence(unlike the legal definition of "Unintentional Manslaughter" in the western law). So it acts like a life insurance.